In general the present invention relates to novel granules and novel methods for manufacturing such granules. In particular aspects, the invention relates to agglomerated granules that contain powder and resin that are homogeneous and compact as well as round and smooth. Such novel granules are useful, inter alia, in the manufacture of fabricated products of superior quality.
Plastic polymers are well-known in the art. Due to their low cost relative to natural materials thermosets and thermoplastics in particular are used extensively in the manufacture of fabricated tiles, table and countertops, walls, floors, fireplaces and an assortment of other products.
These fabricated products are routinely prepared by casting or molding a granular, curable synthetic resin composition that contains a filler. Typically, the synthetic resin constitutes 30%-50% of the mixture by weight, while the filler, and maybe an optional pigment, constitute between 50% and 70% of the mixture. The constituents of the mixture are usually mixed for 20 to 50 minutes and poured into a tray where the mixture is cured, often by the application of heat. Such curing may sometimes lead to xe2x80x9cburningxe2x80x9d, thus rendering the product unusable. After the curing process, which can take hours, the cured material is cooled. In order to obtain granules of a desired size the cured material is broken with hammers or mechanical equipment, ground, and then pulverized. The pulverized material then is classified into different useful granule sizes. The resulting granules typically are not very compact (i.e., contain air-pockets), and are of irregular shapes and surfaces.
It can be appreciated that such methods are labor intensive, expensive, noisy, and grimy. Moreover, a material loss of between 10% and 20% is typically experienced, with xcx9c10% of the material being reduced to an unusable fine powder and another xcx9c10% being lost in the mixing, casting, breaking, and grinding processes.
The present invention provides novel granular compositions and methods used in manufacturing such compositions. Granules of the invention are compact and homogeneous, round and smooth, and can be prepared within a desired range of sizes. Such granules are useful in the manufacture of products that have superior qualities when compared to similar products in the prior art.
According to one aspect of the invention, a method is provided for forming granules of a powder and a liquid. A dry powder is aerated. A liquid is applied to the aerated powder to produce wetted particles of powder. The wetted particles are agglomerated under shear to produce the granules. It has been discovered, unexpectedly, that aerating the powder prior to applying the liquid to the aerated powder results in granules that are densely packed and homogeneous throughout.
In important embodiments of this invention, the method further involves curing the granules to produce cured granules when the liquid is a resin. One independent aspect of the invention is the application of curing conditions during the agglomeration step sufficient to substantially slow or arrest altogether further agglomeration, thereby determining particle size. In one particular embodiment, the agglomeration is carried out relatively slowly, over a period of at least one minute, under agglomeration and curing conditions to produce a batch of particles having an average particle size of between 8 and 140 mesh.
The method also can involve post-curing the granules after agglomeration has been arrested in a location remote from that where the agglomeration took place. Preferably the agglomeration step is carried out under forces sufficient to produce densely packed granules that are free of air bubbles greater than 10 microns in diameter.
The agglomeration can be carried in a variety of well known agglomeration devices, although the preferred device is a rotary blade mixer with 3, dull, spaced mixing blades.
As described in greater detail below, a variety of materials can be added to the powder, to the resin or to an agglomeration chamber to produce a variety of products. Likewise, different liquids other than resin can be applied to the powder to produce a variety of different products, also as discussed in greater detail below. The preferred liquid is a curable resin and the preferred embodiments include curing the granules, preferably during the agglomeration step as described above. In one particularly important embodiment, pigment is added whereby hard granules containing color are produced, such granules can be used in the manufacture of artificial stone products, e.g., counter tops, walls, furniture, cabinets, floors and the like.
According to another aspect of the invention, a method is provided for manufacturing granules of a particular size. The method involves introducing a dry powder into an agglomerator. A liquid resin also is introduced into the agglomerator. Agglomeration conditions are applied in the agglomerator to obtain granules formed of the powder and the resin. In addition, curing conditions are applied within the agglomerator to substantially slow or arrest further agglomeration. The powder is aerated before the liquid resin is added into the agglomerator. The liquid resin is added to the aerated powder either during the agglomeration conditions or before applying the agglomeration conditions. The conditions applied and the materials used are as described briefly above and in greater detail below.
According to another aspect of the invention, products are provided which are produced by any of the methods described above.
According to another aspect of the invention, a cured granule is provided. The granule is made of powder and a cured resin, wherein the surface of the granule is smooth, the shape of the granule is round, and wherein the granule is free of air bubbles having a diameter greater than 10 microns. More preferably, the granule is free of air bubbles having a diameter greater than 5 microns, and in some embodiments, the granule is free of air bubbles having a diameter greater than 1 micron. The granule can be a plurality of such granules formed as a batch or as batches and having an average mesh size of between 8 and 140. Such granules are free flowing. In another embodiment, the granule is free of pockets of unwetted powder. In still another embodiment, the granule contains a homogeneous dispersion of microbubbles having a diameter less than 1 micron. In still another embodiment, the powder can be between 60-95% by weight of the granule and the resin can be between 5-40% of the granule. In one important embodiment, the granule includes pigment and the pigment is present at 0.1-2.0% by weight of the granule. Most preferably, the powder is dispersed homogeneously throughout the granule.
In important embodiments, the granule contains an active agent. As used herein, an active agent is an agent that imparts a desirable property to the granule other than that provided by the powder, the resin and any catalyst for the resin. Thus, active agents can be food additives, natural flavoring agents, antioxidants, acidulants, colorants, odorants, enzymes, fingicides, biocides, nutrients, hormones, cells, chromatography medium, agglutination medium for diagnostics, nephelometric enhancers, immobilization matrices, herbicides, insecticides, pesticides, perfumes, animal feed supplements, fertilizers, surfactants, detergents, immunoassay reagents, and active pharmaceuticals. The granules of the present invention can contain the active agent homogeneously dispersed throughout the cured resin. The active agent can be present in the granule as microparticles. In one important embodiment, the active agent is present by weight of less than xc2xd% or greater than 30% of the total weight of the granule. Prior to the present invention, it was not practical to achieve homogeneous dispersions of active agents below xc2xd% or greater than 30% according to the methodologies used for forming granules in the prior art.
According to still another aspect of the invention, a composite is provided. The composite includes a layer of cured resin having a resin specific gravity, and a plurality of round, cured granules dispersed throughout the cured resin, the cured granules having a granule specific gravity. The cured granules comprise a powder and a cured granule resin with the powder dispersed homogeneously throughout the cured granule resin. In this aspect of the invention, the resin specific gravity is within 10%, and preferably 5%, of the granule specific gravity. Thus, the invention involves new methods for making composites by selecting a resin for forming a layer of a cured resin and forming a plurality of round, cured granules to be dispersed throughout that resin, wherein the cured granules also have a specific gravity and that specific gravity is within 10% of the resin specific gravity. When the cured granules are mixed with the resin as a continuous phase for forming a layer, the cured granules are dispersed throughout the resin and do not float or sink, thereby producing a product with a consistency better than that achieved according to prior art methods.
These and other aspects of the invention are described in greater detail below.